1. Field of the Invention
The present invention relates to the collation of printed sheets and, particularly, to the feeding of individual sheets of paper in the proper order onto a stack of sheets being formed on a conveyor. More specifically, this invention is directed to a feeder station for a machine in which printed sheets are gathered into ordered stacks and, especially, to a feeder station wherein individual sheets caused to move in a first direction upon withdrawal from a supply are subsequently accelerated in a second direction and are thereby caused to be moving when acquired by a pusher mechanism which moves the stack being formed along the path defined by a conveyor. Accordingly, the general objects of the present invention are to provide novel and improved method and apparatus of such character.
2. Description of the Prior Art
While not limited thereto in its utility, the present invention is particularly well suited for use in the manufacture of books. In the assembly of the pages of a book preparatory to binding, it is necessary that the printed sheets comprising the individual pages be processed rapidly while being handled gently. In order to perform this gathering or collating function, apparatus having plural feeder stations which are serially arranged along a path defined by a conveyor are known in the art. In such prior art apparatus, the feeder stations will each have a supporting table to which individual printed sheets, separated from a supply stack, are delivered. These individual sheets are subsequently accelerated from a rest position on the supporting table to the transport speed of the conveyor by means of a pusher element which moves with the conveyor. In the case of high throughput speed, and/or in the case of lightweight sheets, the impact of the pusher element on the edge of the sheet at the beginning of the acceleration cycle may result in the sheet becoming bent or buckled. Any such bending or buckling has the potential of causing malfunction of the collating machine.
In an effort to overcome the above-briefly described problem with prior art collating apparatus, attempts have been made to "pre-accelerate" sheets deposited on feeder station support tables. Restated, it has been proposed to impart motion, in a path generally parallel to that of the gathering conveyor, to a sheet on a feeder station support table prior to its being acquired by a pusher element. An example of such a pre-acceleration arrangement is shown in published German patent DAS 14 86 744. In the arrangement of this German application, a reciprocating motion in the conveying direction is imparted to the supporting tables of the feeder stations of a collating machine. In theory, and providing that sychronization is maintained, the pusher elements will contact a sheet while it is moving with its support table in the downstream direction and thus the pusher element needs only to further accelerate the sheet from the forward speed of the support table to the transport speed of the conveyor. An arrangement of the type shown in German Patent DAS 14 86 744 has the inherent disadvantages that rather expensive apparatus is required and an upper limit on production rate is imposed by the need to impart reciprocating motion to machine elements which necessarily have a mass.
Another approach to providing pre-acceleration to printed sheets may be seen from published German application DAS 29 37 611. A rotating accelerating element is employed in the method and apparatus of this approach. The rotating accelerating element acts against the stationary support table of the feeder station and, upon acquiring a printed sheet resting on the support table, accelerates the sheet in the conveying direction as a consequence of frictional adhesion between the sheet and rotary accelerating element. The reliance upon frictional adhesion suffers from the inherent disadvantages that it may cause twisting of the sheet to be accelerated and often produces marks on the sheet resulting from the pinching thereof between the accelerating element and the stationary support table.
In the case of sheets having a wide format, in order to avoid twisting at the time of acquisition of the sheet by a pusher element of the conveyor, it has been suggested that the rotating accelerating element be given a rod-like configuration and be positioned parallel with the supporting table. Such an arrangement may be seen from published German application DOS 31 26 808.
The previously proposed collating apparatus, wherein a rotary accelerating element was associated with each feeder station support table, require relatively complicated constructions which are volumetrically inefficient. Thus, the space requirements for such constructions preclude their universal use on all prior art collating systems. Also, the initial set-up of such apparatus is very time-consuming, as is their readjustment to each different printed-sheet thickness to be handled. Finally, no means have yet been provided to exclude the possibility of marring of the printed sheets by accelerating roller marks.